(1) Field of the Invention
The present invention relates to the energy storage systems based on zinc-air batteries with rechargeable/replaceable zinc anodes.
(2) Description of the Prior Art
Metal-air batteries are considered prospective devices for energy storage because of low cost, high energy density and no risk of fire or explosion. However zinc-air batteries have numerous problems: electrolyte drying, materials degradation, air electrode clogging, self-discharge, flooding, metal corrosion, growing resistance and poor rechargeability. Many of the mentioned problems have been addressed in this invention.
Zinc, iron, magnesium, aluminum or their alloys can be used in metal-air batteries with replaceable metal anodes. At present only zinc electrodes and their alloys are suitable for practical implementation as components of electrochemically rechargeable metal-air batteries. Zinc is prospective anode material because of sufficiently high battery voltage and rechargeability. An iron-air battery has too small voltage to be considered viable for use in a metal-air battery.
The word “battery” in this application is equivalent to the word “cell” when the number of elementary cells is not specified.
A zinc-air rechargeable battery with a bifunctional air electrode was proposed by Shepard et al., U.S. Pat. No. 4,842,963. The air electrode included oxygen reduction and oxygen evolution catalysts. This application uses a bifunctional air electrode, which is expensive and difficult to optimize for long term operation.
A battery with a replaceable metal anode was developed by Koral et al. U.S. Pat. No. 5,418,090 who suggested a mechanically rechargeable zinc-air battery. The cell could be recharged quickly, however the zinc anode required a complex procedure of recovery.
A battery with dual air electrodes was proposed by Harats and Goldstein U.S. Pat. No. 5,318,861 and Tsai et al. U.S. Pat. No 20050123815. A three electrode battery included an air reduction and oxygen evolution electrodes. The oxygen evolution electrode was positioned inside the cell.
The most attractive property of a zinc-air cell is low cost, however the complexity of the design of the discussed above batteries increases the cost essentially, and makes zinc-air devices less competitive in comparison with lithium batteries.
Burchardt U.S. Pat. No 20080096061 proposed to include metal hydrates as the components of the air electrodes to eliminate zinc-air cell drying.
Yager U.S. Pat. No 20120082907 suggested that anode metal could be deposited on the metal core (for example wire) to form a bundle preferably in form of coil. The presence of an adhesive or a binder as a component of a metal anode results in the increased resistance of the metal anode. A metal anode in form of coil is difficult to arrange in a flat battery to form a storage device with high energy density. The use of current collectors, which are expensive, or catalyze hydrogen evolution, or form insulating oxide layer, or form hydride layer is ineffective from the point of view of price or stability.